Over the years, there has been developed a substantial body of patent and other literature directed to the formation and properties of poly(aryl ethers) (hereinafter called "PAE"). Some of the earliest work such as by Bonner, U.S. Pat. No. 3,065,205, involves the electrophilic aromatic substitution (viz. Friedel-Crafts catalyzed) reaction of aromatic diacylhalides with unsubstituted aromatic compounds such as diphenyl ether. The evolution of this class to a much broader range of PAEs was achieved by Johnson, et al., Journal of Polymer Science, A-1, vol. 5, 1967, pp. 2415-2427; Johnson, et al., U.S. Pat. Nos. 4,108,837; and 4,175,175. Johnson, et al., show that a very broad range of PAE can be formed by the nucleophilic aromatic substitution (condensation) reaction of an activated aromatic dihalide and an aromatic diol.
Thus, PAEs are well known; they can be made from a variety of starting materials, and they can be made with different glass transition temperatures and molecular weights. Nominally, PAEs are transparent and tough, i.e., exhibit high values (&gt;50 ft-lbs/in.sup.2) in the tensile impact test (ASTM D-1822). Their favorable properties class them with the best of the engineering polymers.
Polymer blends have been widely taught and employed in the art. As broad as this statement may be, the blending of polymers remains an empirical art and the selection of polymers for a blend giving special properties is, in the main, an Edisonian-like choice. Certain attributes of polymer blends are more unique than others. The more unique attributes when found in a blend tend to be unanticipated properties.
(a) According to Zoller and Hoehn, Journal of Polymer Science, Polymer Plastics Edition, vol. 20, pp. 1385-1397 (1982):
"Blending of polymers is a useful technique to obtain properties in thermoplastic materials not readily achieved in a single polymer. Virtually all technologically important properties can be improved in this way, some of the more important ones being flow properties, mechanical properties (especially impact strength), thermal stability, and price. PA1 . . . Ultimately, the goal of such modeling and correlation studies should be the prediction of blend properties from the properties of the pure components alone. We are certainly very far from achieving this goal." PA1 "It is well known that compatible polymer blends are rare." PA1 "Miscibility in polymer-polymer blends is a subject of widespread theoretical as well as practical interest currently. In the past decade or so the number of blend systems that are known to be miscible has increased considerably. Moreover, a number of systems have been found that exhibit upper or lower critical solution temperatures, i.e., complete miscibility only in limited temperature ranges. Modern thermodynamic theories have had limited success to date in predicting miscibility behavior in detail. These limitations have spawned a degree of pessimism regarding the likelihood that any practical theory can be developed that can accommodate the real complexities that nature has bestowed on polymer-polymer interactions." PA1 "The vast majority of polymer pairs form two-phase blends after mixing as can be surmised from the small entropy of mixing for very large molecules. These blends are generally characterized by opacity, distinct thermal transitions, and poor mechanical properties. However, special precautions in the preparation of two-phase blends can yield composites with superior mechanical properties. These materials play a major role in the polymer industry, in several instances commanding a larger market than either of the pure components." PA1 "It is well known that, regarding the mixing of thermoplastic polymers, incompatibility is the rule and miscibility and even partial miscibility is the exception. Since most thermoplastic polymers are immiscible in other thermoplastic polymers, the discovery of a homogeneous mixture or partially miscible mixture of two or more thermoplastic polymers is, indeed, inherently unpredictable with any degree of certainty, for example, see P. J. Flory, Principles of Polymer Chemistry, Cornell University Press, 1953, Chapter 13, page 555." PA1 "The study of polymer blends has assumed an ever increasing importance in recent years and the resulting research effort has led to the discovery of a number of miscible polymer combinations. Complete miscibility is an unusual property in binary polymer mixtures which normally tend to form phase-separated systems. Much of the work has been of a qualitative nature, however, and variables such as molecular weight and conditions of blend preparation have often been overlooked. The criteria for establishing miscibility are also varied and may not always all be applicable to particular systems." PA1 "The most commonly used method for establishing miscibility in polymer-polymer blends or partial phase mixing in such blends is through determination of the glass transition (or transitions) in the blend versus those of the unblended constituents. A miscible polymer blend will exhibit a single glass transition between the Tgs of the components with a sharpness of the transition similar to that of the components. In cases of borderline miscibility, broadening of the transition will occur. With cases of limited miscibility, two separate transitions between those of the constituents may result, depicting a component 1-rich phase and a component 2-rich phase. In cases where strong specific interactions occur, the Tg may go through a maximum as a function of concentration. The basic limitation of the utility of glass transition determinations in ascertaining polymer-polymer miscibility exists with blends composed of components which have equal or similar (&lt;20.degree. C. difference) Tgs, whereby resolution by the techniques to be discussed of two Tgs is not possible." PA1 "Perhaps the most unambiguous criterion of polymer compatibility is the detection of a single glass transition whose temperature is intermediate between those corresponding to the two component polymers." PA1 F.sub.c =0 PA1 .phi..sub.1' =.phi..sub.1.sup.1 PA1 .phi..sub.2' =.phi..sub.2.sup.1 PA1 .phi..sub.3.sup.2 =1 PA1 F.sub.c =.chi..sub.AB.sup.C PA1 .chi..sub.c =.phi..sub.j.sup.2 PA1 (1-.chi..sub.c)=.phi..sub.k.sup.2 PA1 .phi..sub.i.sup.1 =1 PA1 All other .phi..sub.i.sup.K =0. PA1 .chi..sub.ij =B.sub.ij for all i & j.